1. Field of the Invention
The invention relates to a one-dimensional optical condensing system which condenses light flux in only one direction so as to form a linear image, and an exposure head which performs exposure by using a linear image formed by the one-dimensional optical condensing system. More particularly, the invention relates to an optical lighting system for correcting light intensity distribution which illuminates a spatial modulator or the like, and an exposure head which performs exposure by using illuminating light emitted by the optical lighting system for correcting light intensity distribution.
2. Description of the Related Art
An optical correcting system for forming a linear image can comprise, for example, a combination of a collimator lens for collimating light flux emitted from a light source and a cylindrical lens having the function of condensing the collimated light flux in only one direction. The above-mentioned one-dimensional optical condensing system is used in, for example, an apparatus which forms a two-dimensional image on a screen by using another optical correcting system for projecting and scanning a linear image formed by the optical condensing system on the screen. The one-dimensional optical condensing system may be used in an exposure head using a one-dimensional spatial modulator.
The above-mentioned one-dimensional optical condensing system has the following problems. When light flux emitted from the light source is circular or elliptical in cross section, a light intensity distribution (i.e., a light quantity distribution) of a linear image, which is formed by condensing the light flux emitted from the light source in one direction, is high at its midsection and low at its peripheral part as shown in FIG. 9. In FIG. 9, the horizontal axis indicates the coordinate of a linear image in the direction in which the linear image is formed with respect to an optical axis, and the vertical axis indicates a light intensity ratio (%).
When light flux emitted from the light source is rectangular in cross section, the light intensity distribution of a linear image is substantially uniform even if the linear image is formed by condensing the light flux in one direction. A rectangular aperture can be provided as a method for forming the cross section of light flux into a rectangular shape. However, a problem exist: more specifically, when the aperture is inserted so as to change circular or elliptical light flux into rectangular light flux, an eclipse of light occurs due to the aperture, and this causes a decrease in the efficiency of use of light.
Moreover, an optical filter having low transmittance at the midsection and high transmittance at the peripheral part can be inserted as a method for making the light intensity distribution of a linear image substantially uniform. However, also in this case, there is a problem, that is, a decrease in the efficiency of use of light of a light flux at the midsection in particular.
The above-mentioned problems of nonuniformity of the light intensity distribution may be involved in, for example, illuminating light for illuminating a two-dimensional spatial modulator for use in an exposure head, as well as light for forming a linear image. For instance, when a laser light source is used as the light source and light flux emitted from the light source is collimated by a collimator so as to use the collimated light flux as illuminating light, the light intensity distribution of the illuminating light is generally the Gaussian distribution, which exhibits a high light intensity at the midsection and a low light intensity at the peripheral part. Thus, the light intensity distribution is non-uniform, and this may prevent excellent exposure.
The invention is designed to overcome the foregoing problems. It is a first object of the invention to provide a one-dimensional optical condensing system which can form a linear image having a substantially uniform light intensity distribution without reducing the efficiency of use of light, and an exposure head which can perform excellent exposure by using a linear image formed by the one-dimensional optical condensing system.
It is a second object of the invention to provide an optical lighting system for correcting light intensity distribution which can obtain illuminating light having a substantially uniform light intensity distribution without reducing the efficiency of use of light, and an exposure head which can perform excellent exposure by using illuminating light emitted by the optical lighting system for correcting light intensity distribution.
A one-dimensional optical condensing system according to a first aspect of the invention, which condenses parallel light flux from a light source in one direction so as to form a linear image, comprises an optical correcting system for correcting light intensity distribution, which changes the width of the light flux at each exit position so that a ratio of an outgoing-light flux width at a peripheral part to an outgoing-light flux width at a midsection near an optical axis may be smaller than a ratio of an incoming-light flux width at the peripheral part to an incoming-light flux width at the midsection; and an optical condensing system which condenses the light flux from the optical correcting system in only one direction, thereby forming a linear image which has a substantially uniform light intensity distribution.
A one-dimensional optical condensing system according to a second aspect of the invention, which condenses light flux in one direction so as to form a linear image, comprises a light source; a collimator lens which collimates light flux emitted from the light source; an optical correcting system for correcting light intensity distribution, which changes the width of the light flux at each exit position so that a ratio of an outgoing-light flux width at a peripheral part to an outgoing-light flux width at a midsection near an optical axis may be smaller than a ratio of an incoming-light flux width at the peripheral part to an incoming-light flux width at the midsection; and an optical condensing system which condenses the light flux from the optical correcting system in only one direction, thereby forming a linear image which has a substantially uniform light intensity distribution.
In the one-dimensional optical condensing system according to the first and second aspects of the invention, parallel light flux enters into the optical correcting system for correcting light intensity distribution. The optical correcting system changes the width of the light flux at each exit position so that a ratio of an outgoing-light flux width at a peripheral part to an outgoing-light flux width at a midsection near an optical axis may be smaller than a ratio of an incoming-light flux width at the peripheral part to an incoming-light flux width at the midsection, thereby performing correction so that a linear image may have a substantially uniform light intensity distribution when the linear image is formed by the parallel light flux. In other words, the incoming light flux having the same width is changed in such a manner that a light flux width at the midsection is expanded, and a light flux width at the peripheral part is reduced. This makes it possible to utilize the light flux at the midsection for the peripheral part, so that the light intensity distribution of the linear image can be made substantially uniform without reducing the efficiency of use of light as a whole.
In the one-dimensional optical condensing system according to the first and second aspects of the invention, the optical correcting system is configured to have refractive power in only the longitudinal direction of the linear image and have no power in the direction perpendicular to the linear image.
In the one-dimensional optical condensing system according to the first and second aspects of the invention, when the optical correcting system is adapted to provide outgoing light flux having the same overall width as the overall width of incoming parallel light flux, a light flux-width at the midsection is expanded, and a light flux width at the peripheral part is reduced.
In the one-dimensional optical condensing system according to the first and second aspects of the invention, when the optical correcting system is adapted to xe2x80x9creducexe2x80x9d the overall width of incoming parallel light flux so as to provide outgoing light flux having a less overall width, the reduction ratio of a light flux width at the midsection may be smaller than the reduction ratio of a light flux width at the peripheral part.
In the one-dimensional optical condensing system according to the first and second aspects of the invention, when the optical correcting system is adapted to xe2x80x9cexpandxe2x80x9d the overall width of incoming parallel light flux so as to provide outgoing light flux having a larger overall width, an expansion ratio of a light flux width at the midsection may be larger than an expansion ratio of a light flux width at the peripheral part.
As described above, the one-dimensional optical condensing system according to the first and second aspects of the invention is applicable regardless of whether light is expanded or reduced in width as a whole or not.
An optical lighting system for correcting light intensity distribution of the invention comprises a light source; a collimator lens which collimates light flux emitted from the light source so as to form illuminating light; an optical correcting system which changes the width of the light flux at each exit position so that a ratio of an outgoing-light flux width at a peripheral part to an outgoing-light flux width at a midsection near an optical axis may be smaller than a ratio of an incoming-light flux width at the peripheral part to an incoming-light flux width at the midsection, thereby forming the illuminating light having a substantially uniform light intensity distribution on a surface to be illuminated.
In the optical lighting system for correcting light intensity distribution of the invention, the collimator lens collimates light flux emitted from the light source, thereby forming illuminating light. The optical correcting system changes the width of the light flux at each exit position so that a ratio of an outgoing-light flux width at a peripheral part to an outgoing-light flux width at a midsection near an optical axis may be smaller than a ratio of an incoming-light flux width at the peripheral part to an incoming-light flux width at the midsection, thereby forming the illuminating light having a substantially uniform light intensity distribution on a surface to be illuminated. Namely, the incoming light flux having the same width is changed in such a manner that a light flux width at the midsection is expanded, and a light flux width at the peripheral part is reduced. This makes it possible to utilize the light flux at the midsection for the peripheral part, so that the light intensity distribution of the linear image can be made substantially uniform without reducing the efficiency of use of light as a whole.
An exposure head according to the first aspect of the invention comprises a one-dimensional optical condensing system according to the second aspect of the invention; a one-dimensional spatial modulator which modulates a linear image formed by the one-dimensional optical condensing system; and an optical image-forming system which forms light flux modulated by the spatial modulator into an image on an exposure surface.
In the exposure head according to the first aspect, a linear image having a light intensity distribution substantially uniformalized by the optical correcting system for correcting light intensity distribution of the one-dimensional optical condensing system is formed on the spatial modulator, and the linear image is modulated by the spatial modulator. The modulated light is formed into an image on the exposure surface by the optical image-forming system. Thus, the image is used to perform exposure. The linear image having the light intensity distribution substantially uniformalized by the optical correcting system for correcting light intensity distribution is used for exposure, and therefore, excellent exposure can be performed without reducing the efficiency of use of light of the whole optical correcting system.
An exposure head according to the second aspect of the invention comprises an optical lighting system for correcting light intensity distribution of the invention; a two-dimensional spatial modulator which modulates illuminating light from the optical lighting system; and an optical image-forming system which forms light flux modulated by the spatial modulator into an image on an exposure surface.
In the exposure head according to the second aspect, the spatial modulator is illuminated by illuminating light having a light intensity distribution substantially uniformalized by the optical correcting system for correcting light intensity distribution of the optical lighting system for correcting light intensity distribution, and the illuminating light is modulated by the spatial modulator. The modulated light is formed into an image on the exposure surface by the optical image-forming system. Thus, the illuminating light is used to perform exposure. The illuminating light having the light intensity distribution substantially uniformalized by the optical correcting system for correcting light intensity distribution is used for exposure, and therefore, excellent exposure can be performed without reducing the efficiency of use of light of the whole optical correcting system.
Other and further objects, features and advantages of the invention will appear more fully from the following description.